This invention relates to a cellulose-derived sponge showing good flexibility even in a dried state and a process for manufacturing same.
As is well known, a cellulose-derived sponge is manufactured from a mixture of viscose, reinforcing fibers such as cotton fibers or hemp fibers, a cell-forming agent, and salt cake. It is also known to add salt cake having a small particle diameter to viscose to such degree that neither salting out nor solidification takes place for the purpose of improving flexibility of a resulting sponge. However, addition of such salt cake is still insufficient. Japanese Patent Publication No. 47-50867 discloses a process of manufacturing a cellulose-derived sponge using latex-containing viscose. The cellulose-derived sponge obtained by this process is still unsatisfactory since elasticity imparted by the remaining latex is insufficient to give a satisfactory flexibility to the cellulose-derived sponge in a dry state. Japanese Unexamined Patent Publication No. 49-74763 discloses a cellulose-derived sponge containing a water-soluble or water-dispersible, high-molecular, hydrophilic, film-forming polymer. However, this sponge shows a poor flexibility.
It is further known to impregnate a plasticizer such as glycerol or propylene glycol in a molded sponge for the purpose of improving flexibility of the sponge in a dried state. Cellulose-derived sponges having impregnated therein a plasticizer show good softness but, once being washed with water, the sponge shows a poor softness after being dried since the plasticizer such as a polyol is washed away. Thus, impregnation of a plasticizer cannot be a substantial dissolution of the problem.